Project Summary/Abstract Establishing a regular breathing pattern and maintaining a stable heart rate after birth is critical for postnatal survival in mammals. Both of these processes depend on normal nervous system development, and failure of either one alone will result in sudden death. The development of neural circuits in the brain that control cardi- orespiratory function can be influenced by both environmental and genetic factors. For example, developmen- tal exposure to nicotine (which activates the cholinergic neurotransmitter system) can impair breathing and heart rate after birth. In addition, selective deletion (knockout) of the Pet-1 gene in mice results in a deficiency of brainstem serotonin (5HT) that is associated with cardiorespiratory abnormalities and increased neonatal mortality. These findings are relevant to human disease since exposure to nicotine-containing cigarette smoke during development is a major risk factor for Sudden Infant Death Syndrome (SIDS), which has been correlat- ed with a deficiency of brainstem 5HT. However, the underlying mechanisms that link nicotine exposure and 5HT deficiency with cardiorespiratory dysfunction and neonatal mortality are not well understood. This gap in knowledge represents a significant problem for understanding the underlying cause of SIDS and perhaps other developmental disorders that impair autonomic behaviors that are essential for postnatal survival. The long- term goal of this research is to understand how brainstem 5HT promotes the normal development and matura- tion of cardiorespiratory control mechanisms. Recent data indicate that developmental exposure to nicotine reverses the breathing deficits that are characteristic of 5HT-deficient Pet-1 knockout mice, but may also in- crease neonatal mortality. This suggests that prolonged exposure to nicotine has differential effects on respira- tory and cardiac control in a 5HT-deficient context. Based on this finding, the central hypothesis of this re- search is that activation of the cholinergic neurotransmitter system via prolonged nicotine exposure compen- sates for the loss of excitatory 5HT inputs to the central neural circuits that control breathing, but destabilizes cardiac rhythm. Using a multi-level approach involving in vivo cardiorespiratory physiology in intact mice and an analysis of respiratory control at two levels of reduced nervous system complexity in vitro, this work will test this hypothesis by pursuing two specific aims: 1) to determine how developmental nicotine exposure normaliz- es breathing behavior in Pet-1 KO mice; and 2) to determine the extent to which developmental nicotine expo- sure impacts neonatal cardiac rhythm in these mice. This approach is innovative because it uses a novel ani- mal knockout model to assess the relationships between prolonged nicotine exposure, cardiorespiratory func- tion and neonatal survival in a 5HT-deficient context. The proposed research is significant as it will provide substantial insight into how the serotonergic and cholinergic neurotransmitter systems interact to promote the development of normal cardiorespiratory control mechanisms and will clarify how exposure to nicotine, a signif- icant health risk due to the prevalence of parental smoking, can contribute to sudden death during infancy.